The importance of hydroxylated forms of vitamin D as regulators of calcium and phosphate metabolism in animals and humans is by now well established through many disclosures in the patent and general literature. Vitamin D.sub.3, the natural form of the vitamin produced in skin, is known to be hydroxylated in vivo to 25-hydroxyvitamin D.sub.3 and then to 1.alpha.,25-dihydroxyvitamin D.sub.3, the latter compound being generally regarded as the tissue-active hormonal form of the vitamin. Likewise, vitamin D.sub.2, which is commonly used as a food additive or vitamin D supplement, undergoes the same hydroxylation sequence in vivo to form 25-hydroxyvitamin D.sub.2 (25-OH-D.sub.2) and 1.alpha.,25-dihydroxyvitamin D.sub.2 (1.alpha.,25-(OH).sub.2 D.sub.2), the latter being essentially as active as 1.alpha.,25-dihydroxyvitamin D.sub.3 in humans and other mammals.
Both 25-OH-D.sub.2 and 1.alpha.,25-(OH).sub.2 D.sub.2, the structures of which are shown below, have been isolated and characterized as metabolites of vitamin D.sub.2 (DeLuca et al., U.S. Pat Nos. 3,585,221; 3,880,894). ##STR1## These metabolites, being derived from vitamin D.sub.2, are characterized by the S-stereochemistry at carbon 24, as shown above.